Japanese Laid-open Patent Publication Nos. 2006-243571 and No. 2005-283932 discuss optical switches used, for example, in wavelength division multiplexing (WDM) ring network connections. The optical switch is an optical device for switching light paths among optical transmission paths, and connects a plurality of WDM ring networks by connecting the WDM ring networks, for example, to physical ports. The optical switch divides received optical signals into a plurality of signals each have different wavelength bands included in the received optical signals, and outputs the divided optical signals to transmission destinations according to the respective wavelengths. When the optical signals are distributed by the optical switch, either the received optical signals (or the optical signals distributed into respective wavelength bands) are outputted from all the output ports (connected WDM ring networks), or the received optical signals (or the optical signals distributed into respective wavelength bands) are outputted from one output port. Hereinbelow, outputting the received optical signals from all the output ports will be referred to as “broadcasting” in the embodiments described herein. Conversely, outputting the received optical signals from one of the output ports will be referred to as “unicasting” in the embodiments described herein. Ring networks are simply referred to as rings in the drawings and in the specification below.
FIG. 18 illustrates an example of optical signal broadcasting with the optical switch to connect a plurality of WDM rings. In the example illustrated in FIG. 18, an optical switch P1 is connected to a ring A, a ring B, a ring C, and a ring D. The optical switch P1 is equipped with an optical coupler (represented as “CPL” in FIG. 18). The received optical signals are transmitted in the form of the original signals to a plurality of transmission destinations. The optical switch P1 in FIG. 18 receives, from the ring A, optical signals including 40 types of wavelengths from wavelength λ1 to wavelength λ40 (hereinbelow, wavelengths λ1-40). The optical switch P1 transmits the optical signals including the same wavelengths λ1-40 as the received optical signals to all the rings (ring B, ring C, ring D) except for the ring A. It is to be noted that the wavelengths λ1-40 depicted in FIG. 18 are provided with numbers to conveniently identify different wavelengths, and thus the numbers do not represent wavelength bands. Moreover, the wavelengths λ1-40 are numbered in order from the smallest wavelength. However, the number of the types of wavelengths is not limited to the 40 types illustrated in FIG. 18.
However, the following problem may occur, for example, if the ring B, ring C, and ring D in FIG. 18 are used by different clients. If the clients that use the rings are different, transmitting the optical signals received from the ring A by broadcasting to the ring B, the ring C, and the ring D involves difficulties with security aspects for the clients. As a result, it is desirable to avoid duplicating the wavelengths of the optical signals transmitted to the ring B, the ring C, and the ring D if each of the clients using the rings are different.
FIG. 19 illustrates an example of optical signal unicasting with an optical switch to connect a plurality of WDM rings. In the example illustrated in FIG. 19, an optical switch P2 is connected to the ring A, the ring B, the ring C, and the ring D as similarly illustrated in FIG. 18. The optical switch P2 is equipped with a wavelength select switch (WSS) and is able to transmit arbitrary wavelengths to a plurality of transmission destinations. In FIG. 19, the optical switch P2 receives optical signals including the wavelengths λ1-40 from the ring A and transmits wavelengths λ1-10 to the ring B, wavelengths λ11-15 and 20 to the ring C, and wavelengths λ16-19, and 21-40 to the ring D, from among the received wavelengths. As illustrated in FIG. 19 when transmitting by unicasting, security problems do not arise even when different clients use the ring B, the ring C, and the ring D since the wavelengths of the optical signals transmitted to the ring B, the ring C, and the ring D are not duplicated.
For example, the optical signals with wavelengths λ1-10 may be transmitted to the ring B and the ring C, but not to the ring D. Transmitting the same optical signals to at least two rings among a plurality of rings connected to the optical switch is referred to as “multicasting” hereinafter. However, the multicasting of optical signals suffers from the following problem.
FIG. 20 illustrates a configuration example when the optical signals with wavelengths λ1-10 are transmitted to the ring B and the ring C in the optical network illustrated in FIG. 19. In the example illustrated in FIG. 20, an optical switch P3 that includes a WSS on the ring A is added as a method, for example, for transmitting the optical signals with wavelengths λ1-10 to the ring B and the ring C. The optical signals with the wavelengths λ1-10 are transmitted to the ring B and the ring C due to the added optical switch P3 transmitting the optical signals with the wavelengths λ1-10 to the ring C.
FIG. 21 illustrates a configuration example when the optical signals with wavelengths λ1-10 are transmitted to the ring B and the ring C in the optical network illustrated in FIG. 19. In the example illustrated in FIG. 21, an optical switch P4 that includes a WSS on the ring B is added as a method, for example, such that the optical signals with wavelengths λ1-10 are transmitted to the ring B and the ring C. The optical signals with the wavelengths λ1-10 reach the ring C due to the added optical switch P4 transmitting the received optical signals with the wavelengths λ1-10 from the ring B to the ring C.
According to either of the methods illustrated in FIG. 20 and FIG. 21, a new optical switch is added and thus there is an increase in the mounting spaces (shelving, units, etc.) for the newly added nodes, in the number of optical fibers for connections, and in the number of setting commands. This leads to increases in initial expenses, operating costs, management costs and the like. Moreover, the network design becomes more complicated.
As illustrated in the example in FIG. 21, a delay may be caused when transmitting the signals with the wavelengths λ1-10 to the ring C by adding the switch P4 equipped with the WSS on the ring B in comparison to transmitting the same optical signals directly from the ring A to the ring C. Although the above explanation uses the example of a ring network, a similar problem arises on other networks such as a linear network.